A Role for microRNA-34a In Regulating CD8alpha+ Dendritic Cell Function

Abstract

Dendritic cells (DCs) play an important role in regulating innate and adaptive immune responses. The CD8alpha+ DC subset is highly efficient at antigen cross presentation and thereby capable of modulating CD8+ T cell activity. In the context of DC activation via ligation of toll-like receptors (TLRs), pathogen-derived antigens are cross-presented on the DCs resulting in CD8+ T cell differentiation into effector cells. One recently identified mechanism for regulation of TLR responses is via microRNAs (miRNAs), which are short non-coding RNAs that regulate gene expression through the RNA interference (RNAi) pathway. While a small set of miRNAs has been linked to DC development and maturation, miRNA regulation of CD8alpha+ DCs has not been investigated.;We generated in vitro cultures of CD8alpha +-like bone marrow derived dendritic cells (CD8alpha+L- BMDCs) that are functionally equivalent to splenic CD8alpha+ DCs. When activated with TLR9 agonist (CpG ODN 1826), these CD8alpha +L-BMDCs express a distinct miRNA signature. We found that miR-34a is highly upregulated in TLR9 activated CD8alpha+L- BMDCs and splenic CD8alpha+ DCs, but not in CD8alpha-L- BMDCs and splenic CD11 b+ CD8alpha+ DCs. Additionally, TLR9 expression is required for miR-34a upregulation by splenic CD8alpha + DCs in response to TLR9 agonist.;Using a miR-34a KO mouse we found that in vitro differentiation, expression of co-stimulatory molecules and production of cytokines and chemokines is comparable in miR-34a KO and wildtype CD8alpha+L- BMDCs in response to TLR9 agonist. However, we observed increased proliferation and activation of OT-I CD8+ T cells cross-primed by ovalbumin loaded miR-34a KO CD8alpha+L- BMDCs. We observed enhanced IL-12 production and increased expression of CD86 by splenic CD8alpha + DCs in miR-34a KO mice after systemic injection of TLR9 agonist. Increased inflammatory cytokine production by cross-primed OT-1 CD8 +T cells in miR-34a KO mice was observed in vivo. These data suggest a role for miR-34a in regulating the function of splenic CD8alpha+ DCs.